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Large-size β-Ga2O3 single crystals without sub-grain boundaries and cracks were grown by the optimized EFG technology. The thermal volatilization of Ga2O3, polycrystalline growth and cracking were systematically characterized and analyzed from phenomenological and crystallographic points. The proportion of CO2 gas in the growth atmosphere and axial temperature gradient of the thermal field play important roles in suppressing the thermal decomposition and volatilization of a Ga2O3 melt. A higher seeding temperature could effectively inhibit polycrystalline growth. Furthermore, the effects of annealing in an oxygen environment on the optical properties of β-Ga2O3 crystals were discussed.

High-quantity and large-size $\beta $ -Ga2O3 single crystals were grown by the optimal edge-defined film-fed method. Under the excitation of 241Am $\alpha $ -ray, the scintillation light yields of the as-grown and after-annealed $\beta $ -Ga2O3 single crystal are estimated to be 4797 and 6788 ph/5.5 MeV- $\alpha $ , respectively. The energy resolutions of the as-grown and after-annealed $\beta $ -Ga2O3 single crystal are 21.8% and 19.1%, respectively. Annealing in the air can eliminate some color centers and decrease the concentration of free electrons, which can lead to the near-infrared absorption. The light yield and the energy resolution are some slightly worse than that of the commercial Bi4Ge3O12 (BGO) scintillator. However, the fast component with the time constant of 7 ns for the as-grown and after-annealed $\beta $ -Ga2O3 single crystal reaches 25% of the total yield, suggesting that the $\beta $ -Ga2O3 single crystal grown by the present method is a promising fast scintillator, which could be used in the ultrafast timing resolution detection systems.

In this investigation, β -Ga2O3 single crystals were grown by the Floating Zone method. At room temperature, the X-ray excited emission spectrum includes ultraviolet and blue emission bands. The scintillation light output is comparable to the commercial BGO scintillator. The scintillation decay times are composed of the dominant ultra-fast component of 0.368 ns and a small amount of slightly slow components of 8.2 and 182 ns. Such fast component is superior to most commercial inorganic scintillators. In contrast to most semiconductor crystals prepared by solution method such as ZnO, β -Ga2O3 single crystals can be grown by traditional melt-growth method. Thus we can easily obtain large bulk crystals and mass production.

Tm-doped (Sc0.5Y0.5)2SiO5 (SYSO) crystals were grown by Czochralski method. The UV-VIR-NIR absorption spectra and the near-infrared emission spectra were measured and analysed by the Judd-Ofelt approach. Temperature influence on both absorption and emission spectra has been determined from the data recorded at room temperature and 10 K. It has been found that the structural disorder resulting from dissimilar ionic radii of Sc3+ and Y3+ in the solid solution (Sc0.5Y0.5)2SiO5 crystal brings about a strong inhomogeneous broadening of Tm3+ ions spectra. However, it affects the excited state relaxation dynamics inherent to thulium-doped Y2SiO5 and Sc2SiO5 hosts weakly.

High quality 0.02 mol%, 0.05 mol%, and 0.08 mol% Fe: β-Ga2O3 single crystals were grown by the floating zone method. The crystal structure, optical, electrical, and thermal properties were measured and discussed. Fe: β-Ga2O3 single crystals showed transmittance of higher than 80% in the near infrared region. With the increase of the Fe doping concentration, the optical bandgaps reduced and room temperature resistivity increased. The resistivity of 0.08 mol% Fe: β-Ga2O3 crystal reached to 3.63 × 1011 Ω ⋅cm. The high resistivity Fe: β-Ga2O3 single crystals could be applied as the substrate for the high-power field effect transistors (FETs).

We investigated the temperature-dependence of X-ray excited luminescence of β-Ga2O3 single crystals. The recombination of free-electrons with self-trapped holes (STHs) responsible for the ultraviolet luminescence (UVL) band was observed. For the as-grown sample with a high electron concentration, the Auger recombination becomes important, which accelerates the decay dynamics and reduces the ultraviolet luminescence band. The ultraviolet luminescence band is controlled by temperature quenching due to the migration of self-trapped holes to VGa3− centers. Annealing in an oxygen environment can increase the VGa3− concentration, which contributes to the blue-green luminescence band when VGa3− captures a self-trapped hole forming a VGa2− center at rising temperature.

The 4-at.% Tm:Sc2SiO5 (Tm:SSO) crystal is successfully obtained by the Czochralski method. The optical properties and thermal conductivity of the crystal are investigated. The broad continuous wave (CW) laser output of (100)-cut Tm:SSO with the dimensions of 3 mm× 3 mm× 3 mm under laser diode (LD)-pumping is realized. The full width at half maximum (FWHM) of the laser emitting reaches up to 21 nm. The laser threshold of Tm:SSO is measured to be 0.43 W. Efficient diode-pumped CW laser performance of Tm:SSO is demonstrated with a slope efficiency of 25.9% and maximum output power of 934 mW.